American Journal of Scientific Research
ISSN 2301-2005 Issue 70 (2012), pp. 5-9
© EuroJournals Publishing, Inc. 2012
http://www.eurojournals.com/ajsr.htm
Study of Optical Properties for
(Lithium Fluoride-Poly-Vinyl Alcohol) Composites
Bahaa H. Rabee
Babylon University, College of Education, Department of Physics, Iraq
Majeed Ali Habeeb
Babylon University, College of Education, Department of Physics, Iraq
E-mail: majeed_ali74@yahoo.com
Ahmed Hashim
Babylon University, College of Education, Department of Physics, Iraq
E-mail: ahmed_taay@yahoo.com
Abstract
In this work , the optical properties of composites of poly-vinyl alcohol(PVA) and
lithium fluoride were prepared by different concentrations of lithium fluoride. Results
showed that the absorbance increases with increase the weight percentage of lithium
fluoride, absorption coefficient, extinction coefficient, refractive index and real and
imaginary parts of dielectric constants are increasing with increase the lithium fluoride
content.
Keywords: Optical properties lithium fluoride, polyvinyl alcohol.
Introduction
Optical properties of polymers constitute an important aspects in study of electronic transition and the
possibility of their application as optical filters, a cover in solar collection, selection surfaces and green
house. The information about the electronic structure of crystalline and amorphous semiconductors has
been mostly accumulated from the studies of optical properties in wide frequency range. The
significance of amorphous semiconductors is in its energy gap[1]. Poly(vinyl alcohol) (PVA), as it is
well known for its interesting behavior and its versatile applications. In water, there exist two possible
intermolecular interactions among PVA chains or between PVA and water, as follows: (1) H-bonding
between modified hydroxyl groups on PVA chains and (2) H-bonding between the —OH groups of
PVA and water molecules[2].
Experimental Procedure
The materials used in this paper are polyvinyl alcohol and lithium fluoride. The weight percentages of
lithium fluoride are (0,5,10 and 15)wt.%. The samples were prepared using casting technique thickness
ranged between (210-418)μm.
The transmission and absorption spectra of PVA-LiF composites have been recording in the
length range (190-850) nm using double-beam spectrophotometer (UV-210oA shimedza ).
Study of Optical Properties for (Lithium Fluoride-Poly-Vinyl Alcohol) Composites
6
Results and Discussion
The variation of absorbance with wavelength of the incident light of composites is shown in figure(1).
The figure shown that no shift in the peak position while the intensity of these peak increased as a
result increase the concentrations of lithium fluoride. .
Figure 1: Variation of Optical absorbance for (PVA-LiF) composite with wavelength
pure
1.2
5 wt.%
10 wt.%
Absorbance
1
15 wt.%
0.8
0.6
0.4
0.2
0
100
200
300
400
500
600
700
800
900
Wavelength(nm)
The absorption coefficient (α) was calculated from the following equation[3]:
A
α = 2.303 .
(1)
d
Where : A is absorbance and d is the thickness of sample.
Figure (2) shows the relationship of the absorption coefficient with photon energy of different
weight percentages of lithium fluoride. The figure shows that the absorption coefficient increases with
increase weight percentages of lithium fluoride, this may be attributed to increase the absorbance with
increasing the concentration of lithium fluoride [3] .
Figure 2: Absorption coefficient for (PVA-LiF) composite with various photon energy
a(cm )-1
p ur e
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
5 wt.%
10 wt.%
15 wt.%
0
1
2
3
4
5
6
7
Photon energy(eV)
The variation of absorption coefficient, α, with the incident photon energy, hν, can be written
as[4] :
(2)
(αhν)n =B(hν −Eg)
where B is an constant depending on the transition probability and n is an index that characterizes the
optical absorption process and is theoretically equal to 1/2,2, 1/3 or 2/3 for indirect allowed, direct
allowed, indirect forbidden and direct forbidden transition, respectively. The usual method to calculate
the band gap energy is to plot a graph between (αhν)n and photon energy, hν, and find the value of the
7
Bahaa H. Rabee, Majeed Ali Habeeb and Ahmed Hashim
n which gives the best linear graph. This value of n decides the nature of the energy gap or transition
involved. If an appropriate value of n is used to obtain linear plot, the value of Eg will be given by
intercept on the hν-axis as shown in figure (3,4).
Figure 3: The relationship between (αhu)1/2 (cm-1.eV) 1/2 and photon energy of (PVA-LiF) composites
18
pure
5 wt.%
(αhυ)1/2(cm-1.eV)1/2
16
10 wt.%
14
15 wt .%
12
10
8
6
4
2
0
0
1
2
3
4
5
6
7
Photon energy(eV)
Figure 4: The relationship between (αhu)1/3 (cm-1.eV) 1/3 and photon energy of (PVA-LiF) composites
pure
7
5 wt.%
10 wt.%
(αhυ)1/3(cm -1.eV)1/3
6
15 wt.%
5
4
3
2
1
0
0
1
2
3
4
5
6
7
Photon energy(eV)
The variation of refractive index
⎡
4 R
n = ⎢
2
⎣ ( R − 1) − k
2
−
R + 1 ⎤
R − 1 ⎥⎦
1
2
of composites with photon
energy as shown in figure(5). The refractive index increases with increase the lithium fluoride
concentrations , this can be attributed to the increasing of the density with increase the concentration of
lithium fluoride [3].
Figure 5: The relationship between refractive index for (PVA-LiF) composite with photon energy
pure
2.8
5 wt .%
2.6
10 wt .%
2.4
15 wt .%
n
2.2
2
1.8
1.6
1.4
1.2
1
0
1
2
3
4
photon energy(eV)
5
6
7
Study of Optical Properties for (Lithium Fluoride-Poly-Vinyl Alcohol) Composites
8
Figure(4) shows the variation of extinction coefficient (k=αλ/4π) with wave length(λ) of
composites as shown in figure(6). The extinction coefficient increases with increasing of lithium
fluoride concentration, this may be attributed to absorption coefficient which increases with increase of
concentration of lithium fluoride [4].
Figure 6: Extinction coefficient for (PVA-LiF) composite with various photon energy
pure
1.4E-05
5 wt.%
10 wt.%
1.2E-05
15 wt .%
1.0E-05
k
8.0E-06
6.0E-06
4.0E-06
2.0E-06
0.0E+00
0
100
200
300
400
500
600
700
800
900
λ(nm)
The relationship between real and imaginary parts of dielectric constants( ε1 =n2-k2and
ε2=2nk)[4] and energy photon of composites are shown in figures(7 ,8).
Figure 7: Variation of real part of dielectric constant (PVA-LiF) composite with photon energy
8
pure
7
5 wt .%
10 wt .%
6
15 wt .%
ε1
5
4
3
2
1
0
0
1
2
3
4
5
6
7
photon energy(eV)
The real and imaginary parts of dielectric constants are increasing with increase the
concentration of lithium fluoride, this related to increase the refractive index and extinction coefficient
with increase the weight percentages of lithium fluoride.
ε2
Figure 8: Variation of imaginary part of dielectric constant(PVA-LiF) composite with photon energy
pure
5.E-05
5.E-05
4.E-05
4.E-05
3.E-05
3.E-05
2.E-05
2.E-05
1.E-05
5.E-06
0.E+00
5 wt .%
10 wt .%
15 wt .%
0
1
2
3
4
photon energy(eV)
5
6
7
9
Bahaa H. Rabee, Majeed Ali Habeeb and Ahmed Hashim
Conclusions
1. The absorbance increases with increase of concentration of lithium fluoride.
2. The absorption coefficient, extinction coefficient, refractive index and real and imaginary parts
of dielectric constants are increasing with increase the weight percentages of lithium fluoride.
References
[1]
[2]
[3]
[4]
Gabriel Pinto and Abdel-Karim Maaroufi, 2011, "Critical filler concentration for electro
conductive polymer composites", Society of Plastics Engineers (SPE), 10.1002/spepro.003521.
Majdi K, Zeedan K. and Attar H., 1997,"Optical properties of poly thiophene/ PVC conducting
polymer alloy films", Iraqi J. of polym., Vol. 1, No. 1,155-162.
Ahmad A.H., Awatif A.M. and Zeid Abdul-Majied N., 2007, "Dopping Effect On Optical
Constants of Polymethylmethacrylate (PMMA)", J. of Eng. & Technology, Vol.25, No.4.
Ahmed R.m. , 2008, "Optical study on poly(methyl methacrylate)/poly(vinyl acetate)", Zagazig
Uni., Zagazig, Egypt, E-mail-rania 8_7@hotmail. com.